DEVELOPMENT OF THE BKAIN. 



681 



floor of the thalamencephalon is ultimately developed into the 

 optic chiasma and part of the optic nerves, as well as the infun- 

 dibulum. The latter comes in contact with a process from the 

 mouth, which is ultimately changed into the pituitary body. The 

 anterior part of the roof of the thalamencephalon becomes very 

 thin, and its place is finally occupied by a vascular plexus, which 



Diagram of a horizontal section of a vertebrate brain. (Huxley.) Olf. 

 Olfactory lobes. L.t. Lamina terminalis. C.S. Corpus striatum. Th. Optic 

 thalamus. Pn. Pineal gland. M.b. Mid-brain. Cb. Cerebellum. M-0. 

 Medulla oblongata. 1. Olfactory ventricle. 2. Lateral ventricle. 3. Hind 

 ventricle. 4. Fourth ventricle, -f- Iter a tertio ad quartum ventriculum. 



persists in the roof of the third ventricle (choroid plexus). The 

 pineal gland a peculiar outgrowth, of unknown function is de- 

 veloped from the posterior part of the roof of the thalamence- 

 phalon, and from its sides, which become extremely thickened, 



are developed the optic thalami. 



57 



